I recently learned of another hosted service -- Qualtrics -- that seems popular among academics and businesses, but I don't really know much about it -- other than the reason I learned about it: Members of a One Laptop per Child (OLPC) list were asked to participate.

Survey Monkey's the only one I've worked with really. (I've rolled a few from scratch a la LAPPP - Linux / Apache / PostgreSQL / PHP / Python, which allows me do do a few cute AJAX-y tricks, but doesn't seem worth the effort.)